Microphone.



J. J. GGMBR.

MICROPHONE.

APPLICATION FILED 11017.28, 1910.

Patented Dec. 2, 1913.

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WIT/M6555 QAM Vv-m?? J. I. COMER.

MICROPHONE.

APPLICATION FILED Nov. z8, 1910.

Patented Dec. 2, 1913.

2 SHEETS-SHEET Z.

UNITED STATES PATIENT OFFICE.;

JOHN J. COMER, or CHICAGO, ILIiINOIs, AssIG'NOR lT o AUTOMATIC'ENUNCIATOR COMPANY, OF CHICAGO, ILLINOIS, A C'oItPOnATION'OF ILLINOIS.

MICROPHONE."

To all whom t may'concem.'

Be it known that I, JOHN J.,COMER', a

citizen of the United States of America., and

resident of Chicago, Cookcounty, lllinois; have invented a certain newand useful Im` provement in Microphones, lofwhi'ch the fol' lowing is aspecification.A

My` invention relates to microphones'wof the so-called differentialtype'. In a microphone of this character, whether involvedl in atransmitter or repeater,` the construction embodies, of course,`anarrangement myself to any particular circuit 'arrange-f ment.

`The object of 5my invention, generally stated, is, therefore, toprovidel a differential microphone of simple and efficient character,adapted'more particularly 'for use in tele phone transmitters. Y

A special Object is yto provide an improved construction and arrangementwhereby the movable electrode ofthe differential microphone may consistof a carbon diaphragm.

Another object is to provide an improved construction and arrangementwhereby' the voice vibrations do not impinge directly upon the center'of the diaphragm ofl the' transmitter, but to the contraryl are4deflected into a restricted space which extends' around the marginalportion yof the dia'- phrag'm, and whereby the latter is vibrated bythealternate compression and rarefaction of the air in saidrestrict'edchamber, caused by the agitation of the'air by the voicevibrations. p It is also an object to provide certa-in details, andfeatures of improvement and combinations tending to increase the geni'eral eiliciency of a diferential microphone lof this particularcharacter.

To the foregoing and other. useful ends, my invention consists inmatters hereinafter set forth and claimed'.

i Specification of Letters Patent.

Application fixed November as, 1910. serial No. 594,419.

` Patented Dee. 2, 1913.

is a longitudinal s'ectiO-nof adi erential microphone transmitterembodying the principles of myr invention, thesaid section being takenon line 14-1 in Fig. 2. Fig. y2`is a -front elevation or face lView 'ofthe said transmit-ter; Fig. 3- is a rear view' of the"saidt-ransi'nitter, with the casing thereof re- .moved to show themicrophone'. F ig'. 4 is `a sectional view showing the dii'lerentpartsof said 'transmitter in separated condition.

As thus'illustrated, my invention com- In the accompanyingdrawings-Figure I' prises acasingA which constitutes tlie'back'4` ofthe'transmitt-er, and a cap or front plate A', ywhich latter has acentral aperture for` the usual `mouth-piece A2. 'lhe inner' disk orplatea is provided with a circular row of holes or apertures-a', andwith `a central and forwardly extending flange 'or rin o2, the'openingof which is closedby the ront A cone ifs extends' forwardintotli'e mouthpiece, and` is of suiiicient area at its baseto fullycover the'plate a4, thus servin` to deflect the 'voice vibrationsoutwardly and through the openings d'5 through which latter they passinto' the thin `or restricted spacca6 that exists between thecarbondia.- phra't'ginja1 and thel back of the lplate a. 'Cardb'oaitlor fiberinsulation as is provided between the plate t and the plate A', and a'ring of similar'insulatioii a9 is interposed between lthe'marginalportions' of the-said plate a andthe diaphragm d?, in the manner shown.A similarring of insulation am is applied to the other side ofthe-diaphragm,

but not directly thereto, the metal ring all" being applied directly tothe diaphra with the insi'ilation 'outside' thereof. T is ring a has aterminal screw a, which screw extends through-theiinsulating ring arl",through the fiber bushing w13, and then through the cardboard or fiberdisk a on the back of the plate a, which latter is similar in allrespects to the plate a, in the manner shown. The-plate or disk al has acentral opening surrounded by a Harige or ring-like `fOr-rnatio'r'i al",the Opening ofthe latter being closed by the carbon back electrode a andthe metal plate als. The

'screwslag and a20 are employed, it will be seen',` for `securing thetwo carbon electrodes to oppositefside's of the box or closure thusAcarbon electrode a3 andthe metal plate a4.

ico

provided and in which is icontained the granularl carbon a, the saidbodyof carbon being dividedinto two portions by the'carv bon diaphragm.There is aspace L22 -between the diaphragm andthe ring or'plate a, whichgives the diaphragm freedom of vibration in a manner that will bereadilyunderstood. Fluffy asbestos or other similar packing a is provided inthe microphone box,l and employed 1n ring form to surround the twobodies o-f granular carbon to prevent leakage of the latter into thespaces a and a when the'y diaphragm is vibrated. Thesuperimposed ringsof metal andcarbon and insulation' are secured tightly together by boltsa2* that extend through them near theouter edges thereof,

y and which bolts are surrounded by fiber insulatio-n or bushing' a2?,whereby said bolts are thoroughly insulated from the structure.

l The terminal a2 is connected with the Plate v'this character is, In,nd, exceedingly etti-- theresult that the air in the thin or re strictcdspace a? vis -alternately compressed andrexhausted or rareied, resultingin a vibrationof the diaphragm. When the dia- 'phrao'm vibrates, itcauses an alternate rise and fall ofthe resistance at opposite sidesthereof, as the resistance through the granular carbon goes up at4 oneside at the same ,time ,that the reslstance goes down at the other side,land vice versa, thus causinga differential variation in the resistanceof the transmitter for the purpose o f generating im ulsesl in thecircult leading therefrom.

differential microphone transmitter of cient and satisfactory in use,and especially adapted kfor .use in loud speaking systems, or systemsofsimilar character. It is capable of carrying a heavyjcurrent, and iscalculated to insure clear enunciation and good tones, whencombined.with proper receiving instruments, and is capable of constant use for along period of time` without the necessity of repair or overhauling. Inother words, and. 1f roperlyadjusted on the l start, it will give ecient and highly satisfactory results for a long time without anyfurther attention. kThe voicevibrations do not impingedirectlyupon thecenter of the diaphragrmbut aregdeflected outwardly and caused to'operateonthe body ofair overly-` ing the marginal portions 'of thediaphragm; whereby better, results are obtained,A-so I ofj saiddiaphragm, withspace between,l the with said apertures, said aperturescoinmuphragm, a circular plate lyin A* the marglnal portions of saidiaphragm, 130

find, than in 4 some .cases where voice vibrations are Ipermittedtolmpmge' directly upon the cente'rof the diaphragm.

lVith-my improved construction, only the diaphragm vibrates. It carriesno weights orheavy parts, and vibrates freely by itself.

What I claim as my invention is:

l. A differential microphone comprising a carbon diaphragm, a pair ofplates, embracing said diaphragm,` .which plates have their outer edgessecured together to clamp the marginal portion ofthe diaphragm betweenthem, with interposed insulation to provide interior spaces betweeen thediaphragmand the two plates, granular carbon engaging theopposite sidesof the diaphragm at the center thereof, and stationary electrodessecured tosaid plates and engaging said granular carbon, said plateslying inclose proximity to said diaphragm.

2. A differential microphone transmitter comprising a diaphragm withoppositely facing electrode surfaces at 'the center thereof, a pair ofplates disposed at opposite sides l plates of the diaphragmvbeingsecured to- -gether at their .outer edges, one of said plates beingprovided with a circular row" of apertures, a mouth piece communicatingl nicating in turn with one of saidl spaces, a @body of granular carbonat each side of; the center of said diaphragm, engag ing said electrodesurfaces, statlonary electrodes engaging said granular carbon, which 10ostationary electrodes are secured to said plates, and a cone shapeddeector in the said mouth-piece, secured at the back of one ofi-saidstationary electrodes,.whereby thel voice -vibrations entering saidmouth-piece are deflected through the said apertures and into the spaceat the front of the diaphragm,

and a springy or resilient packing encircling said granular carbon atopposite sides of said diaphragm to prevent the granular car- 110 bonfrom escaping into. said spaces when the diaphragm is vibrated.

3. In a transmitter, a plate provided with `a circular row of holes, adefiector surrounded by' said circular row of holes, a 115 mouth-pieceinclosing said deector, whereby the voice vibrations are deflectedoutwardly and caused to pass through said openings, a diaphragm back ofsaid row of openings, and rneans covering the central portion of saiddiaphragm to prevent the voice vibrat-ionsfrom` impinging on saidcentral portion, said plate lying in close proximity to the exposedportion of. said diaphragm.

.4. i In a transmitter, a casing, a diaphragm mountedin said casing, acarbon receptacle adjacentto the central portion of said diaadjacent toand a second circular plate on the opposite side of said diaphragm andcovering the marginal portions thereof, said plates being separated fromsaid diaphragm by a narrow air space.

5. In a transmitter, a casing, 'a diaphragm mounted therein, a carbonreceptacle covering the central portion of said diaphragm, and a pair ofcircular plates lying adjacent to said diaphragm on opposite sidesthereof and being'separatedtherefrom by a narrow air space andsubstantially covering the eX- posed surface of said diaphragm.

6. In a transmitter, a casing, a diaphragm mounted therein, a carbonreceptacle covering the central portion of said diaphragm, a pair ofcircular plates lying adjacent to said diaphragm on opposite sidesthereof and being separated therefrom by a narrow air space andsubstantially covering the eX- posed surface of said diaphragm, and aSe.- ries of perforations in one of said plates to permit sound Waves toreach said diaphragrn. i

7 In a transmitter, a casing, a diaphragm mounted therein,- a carbonreceptacle cov'- ering t-he central portion of said diaphragm, a pair ofcircular plates lying adjacent to said diaphragm on opposite sidesthereof and being separated therefrom by a narrow air space andsubstantially covering the eX- vposed surface of said diaphragm, aseries of perforations n one of said plates to permit sound Waves toreach said diaphragm, a mouth-piece secured to said casing, and adefiector insaid mouth-piece for deecting said sound waves through saidperforations.

Signed by me at Chicago, Illinois, this 23d day of November 1910.

, JOHN J. COMER. Witnesses:

S.` LEWIS, E. H. CLEGG.

